Thermo stretch forming of metal



Sept. 13, 1960 B. M. MALONEY THERMO STRETCH FORMING OF METAL Filed May6, 1957 United States Patent G i THERMO STRETCH FORMING OF METAL BartleyM. Maloney, Torrance, Calif., assignor to Northrop Corporation,Hawthorne, Calif., a corporation of 'California Filed May 6, 1957, Ser.No. 657,341

1 Claim. (Cl. 2`19149) This invention has to do with the forming ofmetal .and more particularly with the forming of metal in a stretchvpress and using thermal units to heat certain essential structure.

Historically metal, both eX'trusions and sheet, annealed and hardened,has been formed on stretch presses for a good many years. However, inmost instances the metal has been formed cold or at room temperature.The result of such procedure was that the inherent qualities of themetal resisted forming to accurate tolerances. Hardened metal, whetherit is extruded or in sheet form has created therein, due to stretchforming, certain internal stresses and a certain resilience that resultsin a spring bac when formed in the cold state. The die, when the metalwas formed cold, had to exaggerate the configuration desired in order tocompensate for the spring back or resilience in the metal. Thisprocedure of course could not be applied accurately for the reason thatthe spring back was extremely diiicult to predict and calculate.Therefore, it was necessary to perform hand forming or hammeringoperations, following the stretch forming, in order that the metal couldbe placed in a usable condition. This additional hand forming orhammering operation was particularly costly for the reason that eachpiece had to be done by hand and the time consumed was a decided costelevating factor. Additionally, there was a definite number of piecesthat had to be rejected because no amount of hammering or hand formingcould place them in a usable condition.

An object of this invention is to provide structure that may beincorporated into a stretch press whereby hardened sheet metal orextrusions of metal may be heated to a predetermined temperature and atthe same time the die, of the stretch press, may also be heated to thesame temperature to provide a formed piece of metal that will be wellwithin acceptable tolerances.

Another object of this invention is to provide structure for the thermalstretching of metal and at the same time provide structure for stoppingthe forming of metal at a predetermined moment in order that the formedpiece will be well within acceptable tolerances.

A yet further object of this invention is to provide structure for thethermal forming of metal that is economical, easily installed onexisting equipment and readily operated with a minimum of effort and amaximum benecial result.

Briefly the invention comprises a die having a controlled heatingelement or elements thereon; the metal to be formed has controlled heatapplied to it; and a switch or switches are provided to stop the formingof the metal at the proper moment. This enumerated structure is appliedto a conventional stretch press and related equipment.

Figure 1 is a perspective View illustrating certain structureschematically.

Figure 2 is a fragmentary, cross-sectional view taken on line 2 2 ofFigure l.

P24,952,767 Patented Sept. 13, 1960 Figure 3 is a cross-sectional viewsimilar to Figure 2, but illustrating another form of the invention.

Referring to the drawings for a more detailed description of the presentinvention 10` designates a stretch press die having a conventionalconfiguration. The die is placed upon the bed or table 12 of the pressand a captive holddown bolt or stud 14 is firmly applied to the die toprevent movement thereof during the forming operation.

Each conventional stretch press is provided with a pair of movable metalholding jaws 16, each of which may move in the manner and directionindicated by the arrows. It may be seen that the jaws may stretch andwrap the metal, to be formed, about the die.

Referring to Figures 1 and 2, the die 10 may have a plurality of holestherein into each of which, with one exception, is removably inserted aheater 18. The holes and the heaters are adjacent the working surface 20of the die. Instead of there being a heater in one hole there is a heatsensing element 21 that is connected to a thermostat 22. Obviously eachheater 18` is also connected to the same thermostat through leads 24.Power is supplied the thermostat through a generator 26.

The effect of the described structure is that the die 10 may be heatedto a predetermined temperature and this temperature may be maintainedthrough the entire operation.

The jaws 16 have inserted therein a strip of hardened metal or anextrusion 28 that is to be formed about the working surface 20 of thedie 10. Over the metal material adjacent each end or each jaw' is aheater electrode 30. Power is supplied to the electrode by a resistanceheater 32, having a thermostatic control.

The metal material 28 should be heated to the same temperature as thatof the die 10.

Attention is directed to the fact that the die 10 and the material 28are made of the same material and as a result there is the sameidentical heat of expansion.

The generator 26 may provide 110 volts and the resistance heater 32 mayprovide 440y volts. This feature is not to be considered a limitationfor the reason that other generators and resistance heaters having adifferent potential may also be used.

Attention is directed to the well known fact that each hardened metaland metal alloy has a characteristic that permits the metal to be heatedto a predetermined temperature which results in certain strains orinternal stresses being eliminated when the metal is formed in a stretchpress and the hardened condition retained. As a result the metalmaterial may be stretched and wrapped and the metal will not springback, but will assume and maintain the conguration to which it wasformed.

Referring again to Figure l, a switch 34 is suitably located inrelationship to each jaw 16. The switches are connected to the mainpower source, not shown, to provide a shut off of the stretch press whenthe jaws have reached a predetermined stretch and wrap position. Asillustrated, two switches are shown, but obviously one switch would alsobe applicable.

Figure 3 illustrates a modified form of the heater systern. A groove 36is provided in the die 10 adjacent the working surface 2l)` and anelongated strip-type conventional heater 38 is placed in the groove. Inall other respects that form of the invention illustrated in Figure 3 isidentical to that shown in Figures 1 and 2.

Attention is directed to the fact that the jaws and stretch press properall are suitable and adequately insulated as at 40 and 42 respectively.

The operation of the invention is as follows: The hardened material 28is inserted in the jaws 16. The electrodes 30 are placed over thematerial and the heaters 18 or heater 38 are properly located in the die10. Heat is then applied to the material untila predeterminedtemperature is obtained that corresponds to the previously establishedand maintained temperature of the die. When this temperature vis reachedthe jaws are caused to be moved through'ther path of travel until theswitch or switches 34 are actuated to de-energize the stretch press. Thematerial 28 is then removed from the jaws 16 in the final form. There isabsolutely no spring back as the result of this dened operation andforming procedure.

necessary.

While in order to comply with the statute, the invention has beendescribed in language more or less specific as to structural features,it is to be understood that the invention is not limited to the specificfeatures shown, but that the means and construction herein `disclosedcomprise a preferred form of putting the invention into eifect, and theinvention is therefore claimed in any of its forms or modificationsWithin the legitimate and valid scope of the appended claim.

What is claimed is:

In a stretch press having a die and a pair of movable,

No further hand forming or hammering is l spaced apart jaws that receivemetal materials to be formed into predetermined shapes, the invention ofwhich comprises a plurality of heaters removably received in openings inthe die adjacent the periphery thereof; a controlled resistance heaterremovably attached to each end of said material; means for de-energizingsaid stretch press when said jaws have moved a predetermined distance;and electrical and heat insulating means on said 0 jaws and stretchpress.

References Cited in the file of this patent UNITED STATES PATENTS2,325,481 Crawford July 27, 1943 2,443,336 Waldie lune 15, 19482,493,679 Markey Jan. 3, 1950 2,513,739 ONeill July 4, 1950 2,676,229Knight Apr. 20, 1954 2,783,363 Gunther et al Feb. 26, 1957 2,791,674Westin May 7, 1957 2,808,501 Kilpatrick et al. L.-- Oct. vl, 1957

